TABLE 4.
Strengths and Limitations of Ultrasound Elastography and MR Elastography Techniques for Staging of Liver Fibrosis
| Modality, Implementations | Strengths | Limitations |
|---|---|---|
|
| ||
| Ultrasound | ||
| 1D transient elastography | Relatively inexpensive | Failure and unreliable results due to obesity, narrow intercostal space, ascites |
| Highly portable | Potential classification discrepancies between M, XL, and S probes | |
| Widely available | No anatomic images captured | |
| Independently validated worldwide | No recording of exact measurement location | |
| Used by clinicians at point of service | Narrow applications outside of liver investigation | |
| Shear-wave frequency controlled at 50 Hz | ||
| Little energy absorption by tissues | ||
| Point shear-wave elastography | Permits selection of an ROI on B-mode ultrasound images | More expertise required than 1D transient elastography (requires a radiologist or sonographer) |
| ROI is saved and may be selected in follow-up studies to permit reliable monitoring | Not suitable for point of service | |
| Point shear-wave elastography more robust than 1D transient elastography | Less validated than 1D transient elastography | |
| Generates shear waves inside the liver (more robust) | Greater energy absorption by tissue than 1D transient elastography | |
| Diagnostic performance similar to that of 1D transient elastography | ||
| Low incremental cost of adding required software to an existing scanner | ||
| Shear-wave elastography | Same strengths as point shear-wave elastography techniques | Same limitations as point shear-wave elastography |
| Fast imaging permits generation of quantitative elastograms | Limited availability of this ultrasound system | |
| Numerous ROIs may be positioned on the elastograms | Fewer studies on its diagnostic performance for staging liver fibrosis than 1D transient elastography and point shear-wave elastography | |
| May reduce sampling variability that can occur with 1D transient elastography and point shear-wave elastography | ||
| MRI | ||
| Magnitude of complex shear modulus | Same hardware and software adopted across MRI vendors, which potentially will provide reproducible results | Quality may be degraded in patients with marked iron deposition |
| High diagnostic accuracy for advanced fibrosis | Requires postprocessing and offline analysis | |
| Robust (feasible in larger patients or those with ascites) | Limited availability outside of academic centers | |
| Images a larger proportion of the liver, potentially reducing sampling variability for longitudinal monitoring | Some subjectivity in selecting ROIs | |
| Incremental cost of hardware and software lower than cost of new 1D transient elastography device | Additional time required for positioning the transducer | |
| Low power output and energy absorption by tissues | Acquisition with different breath-holds | |
| Large ROIs not always obtainable because of shear-wave attenuation in normal liver | ||
| Complex (storage modulus and loss modulus) | Multifrequency approach permits calculation of elasticity and viscosity | Currently in research domain |